Ignition device for combustion engines



Nov. 5, 1968 H. 5. BRUIJNING ETAL 3,409,801

IGNITION DEVICE FOR COMBUSTION ENGINES Filed July 6, 1964 FIG.2

H INVENTORJ HUGO sjmuunms .IOHAN L.BAARTNAN BY AGENT United States Patent ()fice 3,409,801 IGNITION DEVICE FOR COMBUSTION ENGINES Hugo Georg Bruijning and Johan Leonard Baartman, Emmasingel, Eindhoven, Netherlands, assignors to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed July 6, 1964, Ser. No. 380,336 Claims priority, application Netherlands, July 4, 1963,

14 Claims. (Cl. 315-209) The invention relates to an ignition device for a combustion engine having at least one high voltage sparkplug.

The ignition devices of this kind hitherto employed comprise an ignition coil having a primary winding or winding portion in which the flow of current is periodically switched on and oif by means of a switch driven by the engine. This winding constitutes a large inductive load for the switch. The contact points of the switch are so heavily loaded, mainly by the high opposite voltage produced across the ignition coil when the circuit thereof is interrupted, that the ignition sparks produced bring about erosion of the contact points. Consequently, the contact points of this switch or interruptor must be replaced periodically, for example, in the case of a motor car after each 10,000 kms.

In the last two decades numerous proposals have been made to replace the interruptor of the ignition device or to materially reduce its load. It has been proposed, for example, to replace the interruptor by an electronic, preferably a semiconductor, circuit element and to control same by pulses produced by some kind of pulse generator. It has been proposed to use an incandescent lamp and a photo-electric cell as the generator. In this case, the engine drives a diaphragm which causes the light of the incandescent lamp to strike the photocell periodically. It has also been proposed to use a small alternating-current generator or an inductor along which a magnet is displaced by the engine.

The photo-electric solution has the disadvantage that an incandescent lamp is required. In order to ensure a reliable and satisfactory light transmission to the photocell, the incandescent lamp, the rotating diaphragm and the photocell must be housed in a small case so as to avoid any deposition of dirt on the incandescent lamp, the photocell or the opening of the diaphragm. This is a diflicult prob lem in itself and the necessity of replacing the incandescent lamp every now and then, since a defect thereof would put the engine out of operation, aggravates the problem and makes it difiicult to find a satisfactory solution for this problem.

The solutions provided by an AC. generator or a rotating magnet have the disadvantage that the control-voltage is heavily produced dependent upon the engine speed and may sometimes be too low, especially at low engine speeds, for example, when the engine is started, in order to ensure reliable operation of the whole ignition device.

An object of the invention is to provide a simple ignition device of the kind set forth in which, at a given position of the engine, there is produced a signal having an amplitude which is independent of the speed of revolution of the engine and which is able to control an elec tronic switch, for example, a thyristor, a gas discharge tube or a power transistor, in a reliable manner.

The ignition device according to the invention is characterized in that the high voltage energy is supplied to the sparkplug under the control of a magnetic switch comprising a bipartite primary winding connected to a source of alternating voltage having a very high frequency compared to the maximum engine speed. Each portion of said primary winding is arranged on a different one of two external limbs of a three-limbed core of ferromagnetic 3,409,801 Patented Nov. 5, 1968 material. The magnetic switch also includes a bipartite secondary winding, each portion of which is arranged on a different one of said external limbs. The two portions of one of said windings are wound in opposite directions. An engine driven armature is provided so as to periodically change considerably the reluctance of the magnetic circuit between the central limb and one of the external limbs of the core, so that the alternating voltage applied to the primary winding intermittently induces a voltage in the secondary winding. a

The invention will be described more fully with reference to the drawing, in which:

FIG. 1 shows a first embodiment of the ignition device according to the invention in a diagrammatic view,

FIG. 2 shows the diagram of a second embodiment, and

FIG. 3 shows an alternative embodiment of the arma: ture.

The ignition device shown in FIG. 1 comprises an ignition coil 1 having a primary winding 2, a secondary winding 3 and a core of ferromagnetic material 4. A charging capacitor 6 is connected between a 200 volt source of direct voltage and ground. Resistor 9 represents the internal resistance of the voltage source. A discharge path for the storage capacitor 6 is provided by means of the primary winding 2 of the coil 1 and an electronic switch 8. The secondary winding 3 is coupled on the one hand with the insulated electrode of a sparkplug 7 and on the other hand to ground, for example, to the chassis of the vehicle driven by the engine. The capacitor 6 is constantly charged by the direct-voltage source.

When the switch 8 is caused to convey current, the capacitor 6 discharges through the primary winding 2 of the ignition coil 1 and induces across the secondary winding 3 a high voltage pulse sufiicient to produce a spark discharged between the electrodes of the sparkplug 7.

In accordance with the invention, the high-voltage energy is supplied to the sparkplug 7 through actuation of the switch 8 under the control of a magnetic switch. The magnetic switch comprises a bipartite primary winding 10, 10, connected to an AC. source having a very high frequency compared to the maximum speed of the engine. With an engine having a maximum speed of 6000 rev./min. rev./sec.), an AC. source of a frequency of at least 36,000 c./s. will provide a sutficiently precise selection of the instant of ignition. At this frequency, one period of the alternating voltage corresponds to a position difference of 1 of rotation of the engine crankshaft.

Each portion of the winding 10, 10' is arranged on a different one of the two external limbs of a three-limbed core 11 of ferromagnetic material. The two portions of the winding are wound in relatively opposite directions as regards the magnetic flux through the central limb of the core 11 so that a current passing through the series-connected winding portions 10 and 10' produces substantially zero net magnetic flux through the central limb of the core 11. The magnetic swtich further comprises a bipartite secondary winding 12, 12' each portion being arranged on a different one of the external limbs of the core 11. The two portions of the secondary winding are connected in series and wound in the same direction as regards the magnetic flux through the central limb of the core 11. The switch also includes an engine-driven armature 13, for example, of a ferromagnetic material having a comparatively high permeability, or of an electrically conductive material, or of both.

When the armature 13 occupies the position shown, it reduces strongly the reluctance of the magnetic circuit comprising the left-hand limb and the central limb of the core 11. Thus a high alternating magnetic flux is produced across said core portion and the alternating voltage induced in the portion 12 of the secondary winding is much greater than the opposite voltage induced in the other portion 12 of the secondary winding. In the opposite position, the armature 13 reduces the reluctance of the magnetic circuit comprising the right-hand limb and the central limb of the core 11, so that the alternating voltage across the portion 12 of the secondary winding is much greater than that across the portion 12' of said winding. In both cases the alternating voltage across the entire secondary winding 12, 12 is applied to the baseemitter circuit of a transistor 14. The emitter-collector circuit of transistor 14 connects the control-electrode of the switch 8 through resistors 15 and 16 to the positive terminal of the direct-voltage source, for example, a 12- volt battery.

When the armature 13 rotates with the same angular speed as the crank shaft of the engine, the device shown is suitable for a 4-cylinder 4-cycle engine or for a Z-cylinder, 2-cycle engine. It may be adapted to any engine by a corresponding modification of the ratio between the speed of revolution of the crank of the engine and that of the armature or'by a modification of the armature itself. If, for example, the armature 13 performs one revolution for every two revolutions of the engine crank shaft, as is common practice with the distributor (not shown) of a 4-cycle 4-cylinder engine, a two-armed star-shaped armature may be used having angles of 90 and 270, respectively, between the arms. Moreover, the rotary shaft of the armature may be displaced to the left or to the right so that it is capable of reducing only the reluctance of the magnetic circuit of the portion of the core 11 comprising the central limb and the left-hand or the right-hand external limb respectively, but is not capable of reducing that of the other magnetic circuit comprising the righthand or the left-hand external limb, respectively, of the core 11. In this case a four-armed, star-shaped armature having angles of 90 between the arms may be used, as shown in FIG. 3.

The switch 8 is a semi-conductor controlled rectifier. The emitter of rectifier 8 is connected to ground and the anode is connected through the primary winding 2 of the ignition coil 1 to the positive terminal of the capacitor 6. The ignition electrode (control-electrode) of the rectifier is connected through the current-limiting resistor 15 to the collector of a PNP amplifying transistor 14. The resistor 16 in the emitter circuit of the transistor 14 serves for stabilizing the working point of this transistor.

The aforesaid alternating-voltage source is an oscillator comprising a p-n-p transistor 17, a resonant circuit comprising inductor 18 and capacitor 19 connected between the collector of said transistor and ground, a feedback windin g 20 included in the emitter circuit of said transistor and arranged on the same core 21 of ferromagnetic material as the winding of the inductor 18 of the resonant circuit 18, 19, and means for determining the working point. In parallel with the resonant circuit 18, 19 there is connected the primary winding 10, 10 of the magnetic switch by way of a coupling capacitor 30.

The means for determining the working point of the oscillator includes a resistor 22 shunted by a capacitor 23 and connected in series with the feedback winding 20 in the emitter circuit of the transistor 17. Resistor 22 and capacitor 23 are connected between the winding 20 and the positive terminal of the direct-voltage source of 12 v. An ohmic voltage divider comprising serially connected resistors 24 and 25 is connected across said direct-voltage source. The junction of resistors 24 and 25 is connected to the common junction of the winding 20 and the resistor 22 by means of a diode 26 connected in the reverse direction. When the temperature increases, the collector leakage current .L, and hence also the emitter current of the transistor 17 tend to increase. The leakage current of the diode 26, however, also increases so that the voltage across the resistor 22 increases and the increase in the emitter current of the transistor 17 is counteracted. Finally, the base of the transistor 17 is connected to the junction of two resistors 27 and 28, which are in turn connected 4 to the 12-volt direct voltage source in series with a diode 29 connected in the forward direction.

Normally, the transistor 17 is driven in the forward direction by means of the said working-point-determining members so that the oscillator circuit including this transistor can freely oscillate. At the instant when the thyristor 8 again becomes non-conducting subsequent to the discharge of the capacitor 6, the potential at its anode rises along with the positive terminal of the capacitor 6. This potential variation is applied through a capacitor 31 and a series resistor 32 to the diode 29, which is thus cut otf. The result is that a positive bias voltage is transiently applied to the base of the transistor 17 so that the latter is out Oh and the oscillator can no longer oscillate for a short time. As a result, the transistor 14 remains cut off so that the thyristor 8 cannot be ignited prematurely by a stray transmission of the oscillations of the oscillator before the capacitor 6 has been recharged to the full voltage of the ZOO-volt direct-voltage source.

Of course, as an alternative, the transistor 14 could be cut off in the same manner during the restoring time of the thyristor 8 and the charging time of the capacitor 6, but cutting-cit of the oscillator transistor 17 has been found in practice to be more reliable.

Alternatively, the winding portions 10 and 10' may be wound in the same direction and the winding portions 12 and 12' in opposite directions. The voltages produced across the winding portions 12 and 12 in the high reluctance position of the ferromagnetic armature element would then neutralise each other substantially, whereas in the low reluctance position of the armature element, the voltage across one of said winding portions, for example, 12', is muchgreater than that across the other portion. Nevertheless, the device was found to be more reliable when the winding portions 10 and 10 are wound in opposite directions, so that substantially no magnetic flux is produced in the control limb of the core as long as zero transmission is to take place via the magnetic switch.

The embodiment shown in FIG. 2 differs from that shown in FIG. 1 in that the oscillator circuit including the transistor 17 is employed, for controlling through the magnetic switch 1013, an amplifier which feeds amplified A.C. impulses to the primary winding 2 of the ignition coil 1. The sparkplug 7 is thus supplied with high voltage A.C. pulses by the ignition coil 1. To this end the ignition coil 1 must be of a special structure related to the frequency of the oscillator circuit including the transistor 17, i.e., it must have a low capacitance and a natural resonance frequency considerably higher than the oscillator frequency. Alternatively, a frequency-dividing amplifier may be included, for example, between the magnetic switch 10 to 13 and the input electrodes of the transistor 14.

The armature 13 of this embodiment rotates about a shaft which is parallel to the air gap between the central limb and the left-hand external limb of the core 11. This provides a variation of the reluctance of the core 11 which is steeper and more accurately fixed in time. When this armature is driven with the same speed of revolution as the distributor (not shown) of the engine, the number of limbs is equal to the number of cylinders of said engine.

The transistor 14 must be capable of supplying the ignition energy and therefore requires the use of a power transistor, for example, an ASZ 18. In order to obtain an adequate control of the power transistor by means of the magnetic switch, the latter is simultaneously employed as a voltage step-up transformer having a ratio of, for example, 1:10 between the primary winding 10, 10 and the secondary winding 12, 12'. The low impedance primary winding is included in the emitter circuit of the oscillator transistor 17 in series with the elements 22 to 26 for determining the working point and for the stabilisation. The feedback winding 20 is then included in the base circuit of the transistor 17. The base potential thereof is determined by the voltage divider 27, 28 and stabilised by a capacitor 33. g

Finally, the control-voltage is applied to the baseof the transistor 14 through a Zener diode 34. The base electrode in turn is connected to the +12 volt terminal through a resistor 36. The emitter circuit includes a diode 37, raising the natural threshold, so that the transistor cannot respond to interference voltages and remains cut off, except in the case of a strong transmission of the oscillations through the magnetic switch to 13. i

In a practical embodiment of the kind shown in FIG. 1, the ignition coil 1 was of the conventional type;

The thyristor 8 was a CIOD by General Electric.

'lhe transistor 14 was an OCY12 and the transistor 17 an OCSO. The diode 26 was an 0A5 and the diode 29 an OA200.

The winding portions 10 .and 10 had 75 turns each and the winding portions 12 and 12' 150 turns each. The inductor 18 had 300 turns and the feedback winding20 had 15 turns. v p

The resistors and capacitors'had the following values:

and the oscillator frequency amounted to about 30,000 c./s.

What is claimed is:

1. An ignition system for an internal combustion engine having at least one spark plug coupled to a high voltage ignition coil comprising, a three-limbed core of ferromagnetic material comprising a central limb and a pair of outer limbs, a first bipartite winding comprising a first winding section mounted on one of said outer limbs and a second winding section mounted on the other of said outer limbs, a second bipartite winding comprising a first winding section mounted on one of said outer limbs and a second winding section mounted on the other of said outer limbs, the first and second winding sections of one of said bipartite windings being wound in opposite directions, a source of alternating voltage coupled to said first bipartite winding and having a frequency which is high relative to the maximum engine speed, a ferromagnetic armature rotated in synchronism with the engine and positioned adjacent the limbs of said core so as to bridge no more than one pair of limbs at any given instant during said rotation, said armature being operative to peri odically vary the reluctance of the magnetic circuit comprising the central limb and at least one of said outer limbs of the core so that the alternating voltage applied to said first bipartite winding induces discrete voltage pulses in said second bipartite winding, and means responsive to said induced pulses for energizing said ignition coil to produce high voltage electric ignition pulses for said sparkplug in synchronism with the engine rotation.

2. A system as described in claim 1 wherein said armature comprises one or more arms arranged in the form of a star about its axis of revolution, said armature being rotatively driven by the engine so that each of the arms alternately reduces the reluctance of the magnetic circuits comprising the central limb and each of the two outer limbs of the core, respectively, during each revolution of the armature.

3. A system as described in claim 1 wherein said arma ture comprises one or more arms projecting about its axis of revolution, said armature being positioned so that said axis of revolution is approximately coaxial with the axis of the central limb of the core and being rotatively driven by the engine so that each armature arm alternately reduces the reluctance of the magnetic circuits comprising the central limb and'each of the two outer limbs, respectively, whereby two alternating voltage pulses are induced in said second bipartite winding by each of said arms during each revolution of the armature.

4. An ignition system as described in claim 1 wherein said first and second oppositely wound winding sections comprise the winding sections of said first bipartite 'winding and wherein said armature rotates so as to vary the length of the air gap between said central limb and at least one of said outer limbs and thereby the reluctance of said magnetic circuit, said first bipartite winding sections being series connected so that in the maximum reluctance position of the armature the magnetic flux produced in said central limb by current flow in said first bipartite winding first winding section is substantially compensated by the magnetic flux produced therein by said current flow in said first bipartite winding second winding section.

5. An ignition system as described in claim 1 wherein said first and second oppositely wound winding sections comprise the winding sections of said first bipartite winding and wherein said first and second winding sections of said second bipartite winding are relatively wound in the same direction, said armature being rotatable so as to cyclically vary the length of the air gap between said central limb and at least one of said outer limbs and thereby the reluctance of said magnetic circuit, whereby unequal and opposite voltages are induced in said first and second winding sections of said second bipartite winding in the minimum reluctance position of said armature.

6. A system as described in claim 1 wherein said coil energizing means comprises, controlled rectifier means coupled to said ignition coil for periodically applying eletric current pulses thereto, and amplifying means electrically interposed between said second "bipartite winding and the control electrode of said controlled rectifier means for controlling conduction therein in response to said induced voltage pulses, means controlled by the current pulses flowing in said controlled rectifier means for producing unidirectional voltage pulses, and means for applying said unidirectional voltage pulses to said amplifying means in the reverse bias direction so as to suppress premature ignition of said controlled rectifier means.

7. A system as described in claim 6 wherein said coil energizing means further comprises a storage capacitor, a source of direct voltage for charging said capacitor, means connecting said capacitor, a portion of said ignition coil and said controlled rectifier means in series circuit thereby to provide a discharge path for said capacitor which is closed in synchronism with said induced voltage pulses.

8. A system as described in claim 1 wherein said coil energizing means comprises controlled rectifier means coupled to said ignition coil for applying electric current pulses thereto in synchronism with said induced voltage pulses, means for coupling said second bipartite winding to the control electrode of said controlled rectifier means for controlling the conduction therein in response to said induced voltage pulses, said source of alternating voltage comprising a high frequency oscillator including amplifying means, means controlled by the current pulses fiowing in said controlled rectifier means for producing unidirectional voltage pulses, and means for applying said unidirectional voltage pulses to said amplifying means in the reverse bias direction so as to suppress oscillations therein during the periods between the high voltage ignition pulses.

9. In an ignition system for an internal combustion engine having a high voltage ignition coil and at least one sparkplug coupled thereto, a voltage pulse generator com- 7 prising a core of ferromagnetic material having three parallel coplanar limbs projecting from a base portion and arranged to form a first magnetic circuit comprising the central limb and one outer limb of the core and a second magnetic circuit comprising said central limb and the other outer limb of the core, a first bipartite Winding comprising first and second identical winding sections coupled with said first and second magnetic circuits, respectively, a second bipartite winding comprising third and fourth identical winding sections coupled with said first and second magnetic circuits, respectively, the winding sections of one of said bipartite windings being wound in opposite directions, a high frequency oscillator coupled to said first bipartite winding, a ferromagnetic armature rotated in synchronism with the engine and positioned adjacent the limbs of said core so as to bridge no more than one pair of limbs at any given instant during said rotation, said armature being rotatable about an axis that lies in the plane formed by the limbs of said core thereby to alternately vary the reluctance of said first and second magnetic circuits and synchronously induce in said second bipartite winding high frequency electric pulses of substantially constant amplitude independent of engine speed, and means for supplying said induced electric pulses to said ignition coil at regular intervals to produce synchronized high voltage pulses of constant amplitude for said sparkplug at all engine speeds.

10. A source of synchronized voltage pulses for the ignition coil of an internal combustion engine comprising, a three-limbed core of ferromagnetic material comprising a central limb and first and second outer limbs, a first bipartite winding comprising first and second serially connected winding sections mounted on said first and second outer limbs, respectively, a second bipartite winding comprising third and fourth serially connected winding sections mounted on said first and second outer limbs, respectively, the winding sections of one of said bipartite windings being wound in opposite directions, a source of alternating voltage coupled to said first bipartite winding and having a frequency which is high relative to the maximum engine speed, an armature positioned adjacent the limbs of said core and arranged to rotate about a point adjacent said central limb in synchronism with the engine so as to alternately effectively open and close the magnetic circuits comprising said central limb and said first and second outer limbs, respectively, thereby to vary the magnetic coupling between said first and second bipartite windings to synchronously induce voltage pulses in said second bipartite winding, and means responsive to said induced voltage pulses for supplying electric pulses to said ignition coil to produce synchronized high voltage pulses for the engine sparkplugs.

11. Apparatus as described in claim 10 wherein said three-limbed core comprises an E-shaped member and said armature is arranged to rotate in a plane perpendicular to the limbs of said E-shaped member.

12. A system as described in claim 1 wherein said source of alternating voltage comprises a high frequency oscillator, said system further comprising means for producing a unidirectional voltage pulse subsequent to each ignition pulse, and means for applying said unidirectional pulse to said oscillator during the interval between successive ignition pulses and in a sense so as to reverse bias the oscillator and suppress oscillation thereof during said interval.

13. An ignition system for an internal combustion engine comprising, a high voltage ignition coil, an E-shaped core of ferromagnetic material comprising a center limb and first and second outer limbs which together form first and second air gaps, a first bipartite winding comprising first and second serially connected winding sections mounted on said first and second outer limbs, respectively, a second bipartite winding comprising third and fourth serially connected winding sections mounted on said first and second outer limbs, respectively, the winding sections of one of said bipartite windings being wound in opposite directions, a source of alternating voltage coupled to said first bipartite winding, a ferromagnetic armature rotated in synchronism with the engine and positioned adjacent the limbs of the core so as to periodically bridge only one of said air gaps during said rotation, said armature being operative in said one air gap to periodically vary the reluctance thereof so as to synchronously induce in said second bipartite winding electric pulses of the frequency of said alternating voltage, and means for coupling said second bipartite winding to said ignition coil.

14. An ignition system as described in claim 13 wherein the length of said armature is substantially equal to the length of said one air gap and wherein said armature is arranged to rotate in a plane perpendicular to the plane formed by the limbs of said E-shaped member about an axis that is parallel to said one air gap.

References Cited UNITED STATES PATENTS 2,726,544 12/ 1955 Anastasia 328-1 2,918,913 12/ 1959 Guiot. 3,161,803 12/ 1964 Knittweis. 3,229,210 1/1966 Frank et al. 328-1 3,277,340 10/1966 .lukes et al. 315218 JOHN W. HUCKERT, Primary Examiner.

J D. CRAIG, D. O. KRAFT, Assistant Examiners. 

1. AN IGNITION SYSTEM FOR AN INTERNAL COMBUSTION ENGINE HAVING AT LEAST ONE SPARK PLUG COUPLED TO A HIGH VOLTAGE IGNITION COIL COMPRISING, A THREE-LIMBED CORE OF FERROMAGNETIC MATERIAL COMPRISING A CENTRAL LIMB AND A PAIR OF OUTER LIMBS, A FIRST BIPARTITE WINDING COMPRISING A FIRST WINDING SECTION MOUNTED ON ONE OF SAID OUTER LIMBS AND A SECOND WINDING SECTION MOUNTED ON THE OTHER OF SAID OUTER LIMBS, A SECOND PIPARTITE WINDING COMPRISING A FIRST WINDING SECTION MOUNTED ON ONE OF SAID OUTER LIMBS AND A SECOND WINDING SECTION MOUNTED ON THE OTHER OF SAID OUTER LIMBS, THE FIRST AND SECOND WINDING SECTIONS OF ONE OF SAID BIPARTITE WINDINGS BEING WOUND IN OPPOSITE DIRECTIONS, A SOURCE OF ALTERNATING VOLTAGE COUPLED TO SAID FIRST BIPARTITE WINDING AND HAVING A FREQUENCY WHICH IS HIGH RELATIVE TO THE MAXIMUM ENGINE SPEED, A FERROMAGNETIC ARMATURE ROTATED IN SYNCHRONISM WITH THE ENGINE AND POSITIONED ADJACENT THE LIMBS OF SAID CORE SO AS TO BRIDGE NO MORE THAN ONE PAIR OF LIMBS AT ANY GIVEN INSTANT DURING SAID ROTATION, SAID ARMATURE BEING OPERATIVE TO PERIODICALLY VARY THE RELUCTANCE OF THE MAGNETIC CIRCUIT COMPRISING THE CENTRAL LIMB AND AT LEAST ONE OF SAID OUTER LIMBS OF CORE SO THAT THE ALTERNATING VOLTAGE APPLIED TO SAID FIRST BIPARTITE WINDING INDUCES DISCRETE VOLTAGE PULSES IN SAID SECOND BIPARTITE WINDING, AND MEANS RESPONSIVE TO SAID INDUCED PULSES FOR ENERGIZING SAID IGNITION COIL TO PRODUCE HIGH VOLTAGE ELECTRIC IGNITION PULSES FOR SAID SPARKPLUG IN SYNCHRONISM WITH THE ENGINE ROTATION. 